A typical roof here lands around 5.0 kW, with most eligible homes comfortably fitting within 3–6 kW. Each kilowatt of panels produces roughly 866 kWh per year on a south-facing roof. We value self-used electricity at 27.1p and exported surplus at a baseline 10p via SEG. Use the calculator above for your exact tariff.
Browse the scenarios below. Each battery size has its own expand — open the one that matches your plan (or just explore). For each system size (2–8 kW) we show annual output, how much you use directly, what gets exported, annual benefit, upfront cost, break-even, and a 20-year net. Negative numbers are possible — that’s the honest trade-off when adding more battery than your usage profile justifies.
No battery 5 kW example → Annual benefit: £729, Upfront: £10,173, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1732 kWh | 693 kWh | 1039 kWh | £187 | £104 | £291 | £4,069 | 14.0 yrs | £1,759 |
| 3 kW | 2598 kWh | 1039 kWh | 1559 kWh | £281 | £156 | £437 | £6,104 | 14.0 yrs | £2,639 |
| 4 kW | 3464 kWh | 1386 kWh | 2078 kWh | £375 | £208 | £583 | £8,138 | 14.0 yrs | £3,518 |
| 5 kW | 4330 kWh | 1732 kWh | 2598 kWh | £469 | £260 | £729 | £10,173 | 14.0 yrs | £4,398 |
| 6 kW | 5196 kWh | 2078 kWh | 3118 kWh | £562 | £312 | £874 | £12,207 | 14.0 yrs | £5,277 |
| 7 kW | 6062 kWh | 2425 kWh | 3637 kWh | £656 | £364 | £1,020 | £14,242 | 14.0 yrs | £6,157 |
| 8 kW | 6928 kWh | 2771 kWh | 4157 kWh | £750 | £416 | £1,166 | £16,276 | 14.0 yrs | £7,036 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
3 kWh battery 5 kW example → Annual benefit: £876, Upfront: £12,273, Break-even: 14.0 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1732 kWh | 1039 kWh | 693 kWh | £281 | £69 | £351 | £6,169 | 17.6 yrs | £841 |
| 3 kW | 2598 kWh | 1559 kWh | 1039 kWh | £422 | £104 | £526 | £8,204 | 15.6 yrs | £2,312 |
| 4 kW | 3464 kWh | 2078 kWh | 1386 kWh | £562 | £139 | £701 | £10,238 | 14.6 yrs | £3,782 |
| 5 kW | 4330 kWh | 2598 kWh | 1732 kWh | £703 | £173 | £876 | £12,273 | 14.0 yrs | £5,253 |
| 6 kW | 5196 kWh | 3118 kWh | 2078 kWh | £844 | £208 | £1,052 | £14,307 | 13.6 yrs | £6,723 |
| 7 kW | 6062 kWh | 3637 kWh | 2425 kWh | £984 | £242 | £1,227 | £16,342 | 13.3 yrs | £8,194 |
| 8 kW | 6928 kWh | 4157 kWh | 2771 kWh | £1,125 | £277 | £1,402 | £18,376 | 13.1 yrs | £9,664 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
5 kWh battery 5 kW example → Annual benefit: £950, Upfront: £13,673, Break-even: 14.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1732 kWh | 1212 kWh | 520 kWh | £328 | £52 | £380 | £7,569 | 19.9 yrs | £32 |
| 3 kW | 2598 kWh | 1819 kWh | 779 kWh | £492 | £78 | £570 | £9,604 | 16.8 yrs | £1,798 |
| 4 kW | 3464 kWh | 2425 kWh | 1039 kWh | £656 | £104 | £760 | £11,638 | 15.3 yrs | £3,564 |
| 5 kW | 4330 kWh | 3031 kWh | 1299 kWh | £820 | £130 | £950 | £13,673 | 14.4 yrs | £5,330 |
| 6 kW | 5196 kWh | 3637 kWh | 1559 kWh | £984 | £156 | £1,140 | £15,707 | 13.8 yrs | £7,096 |
| 7 kW | 6062 kWh | 4244 kWh | 1819 kWh | £1,148 | £182 | £1,330 | £17,742 | 13.3 yrs | £8,862 |
| 8 kW | 6928 kWh | 4850 kWh | 2078 kWh | £1,312 | £208 | £1,520 | £19,776 | 13.0 yrs | £10,628 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
7.5 kWh battery 5 kW example → Annual benefit: £972, Upfront: £15,423, Break-even: 15.9 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1732 kWh | 1264 kWh | 468 kWh | £342 | £47 | £389 | £9,319 | 24.0 yrs | £-1,541 |
| 3 kW | 2598 kWh | 1897 kWh | 701 kWh | £513 | £70 | £583 | £11,354 | 19.5 yrs | £314 |
| 4 kW | 3464 kWh | 2529 kWh | 935 kWh | £684 | £94 | £778 | £13,388 | 17.2 yrs | £2,169 |
| 5 kW | 4330 kWh | 3161 kWh | 1169 kWh | £855 | £117 | £972 | £15,423 | 15.9 yrs | £4,023 |
| 6 kW | 5196 kWh | 3793 kWh | 1403 kWh | £1,026 | £140 | £1,167 | £17,457 | 15.0 yrs | £5,878 |
| 7 kW | 6062 kWh | 4425 kWh | 1637 kWh | £1,198 | £164 | £1,361 | £19,492 | 14.3 yrs | £7,733 |
| 8 kW | 6928 kWh | 5058 kWh | 1871 kWh | £1,369 | £187 | £1,556 | £21,526 | 13.8 yrs | £9,587 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
10 kWh battery 5 kW example → Annual benefit: £987, Upfront: £17,173, Break-even: 17.4 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1732 kWh | 1299 kWh | 433 kWh | £352 | £43 | £395 | £11,069 | 28.0 yrs | £-3,172 |
| 3 kW | 2598 kWh | 1949 kWh | 650 kWh | £527 | £65 | £592 | £13,104 | 22.1 yrs | £-1,259 |
| 4 kW | 3464 kWh | 2598 kWh | 866 kWh | £703 | £87 | £790 | £15,138 | 19.2 yrs | £655 |
| 5 kW | 4330 kWh | 3248 kWh | 1083 kWh | £879 | £108 | £987 | £17,173 | 17.4 yrs | £2,569 |
| 6 kW | 5196 kWh | 3897 kWh | 1299 kWh | £1,055 | £130 | £1,184 | £19,207 | 16.2 yrs | £4,483 |
| 7 kW | 6062 kWh | 4547 kWh | 1516 kWh | £1,230 | £152 | £1,382 | £21,242 | 15.4 yrs | £6,396 |
| 8 kW | 6928 kWh | 5196 kWh | 1732 kWh | £1,406 | £173 | £1,579 | £23,276 | 14.7 yrs | £8,310 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
13.5 kWh battery 5 kW example → Annual benefit: £1,002, Upfront: £19,623, Break-even: 19.6 yrs
| System | Annual output | Self-use | Exported | Bill saving | Export income | Annual benefit | Upfront cost | Break-even | 20-year net |
|---|---|---|---|---|---|---|---|---|---|
| 2 kW | 1732 kWh | 1334 kWh | 398 kWh | £361 | £40 | £401 | £13,519 | 33.7 yrs | £-5,504 |
| 3 kW | 2598 kWh | 2001 kWh | 598 kWh | £541 | £60 | £601 | £15,554 | 25.9 yrs | £-3,531 |
| 4 kW | 3464 kWh | 2667 kWh | 797 kWh | £722 | £80 | £801 | £17,588 | 21.9 yrs | £-1,559 |
| 5 kW | 4330 kWh | 3334 kWh | 996 kWh | £902 | £100 | £1,002 | £19,623 | 19.6 yrs | £414 |
| 6 kW | 5196 kWh | 4001 kWh | 1195 kWh | £1,083 | £120 | £1,202 | £21,657 | 18.0 yrs | £2,387 |
| 7 kW | 6062 kWh | 4668 kWh | 1394 kWh | £1,263 | £139 | £1,403 | £23,692 | 16.9 yrs | £4,360 |
| 8 kW | 6928 kWh | 5335 kWh | 1594 kWh | £1,444 | £159 | £1,603 | £25,726 | 16.0 yrs | £6,333 |
Assumptions: south-facing, sensible tilt; self-use shares from site rules; export at 10p baseline. Costs: panels £/kW = 2,035, battery £/kWh = 700.
Figures are illustrative and use the same method as the calculator above. For exact results, adjust your roof direction, tariff, and usage in the calculator.